Valve mechanism of engine

Abstract

A valve mechanism for an engine includes a camshaft, a rocker arm, a synchronization cam that rotates in synchronism with a valve driving cam, and a switch assembly that switches the driving state of an intake valve or an exhaust valve when a cam follower is pressed by the synchronization cam. The synchronization cam presses the cam follower at a time when the intake valve or the exhaust valve is closed. The switch assembly includes a switch unit that switches the driving state when a switch moves, a driver that drives the switch via a transmission, and a positioner including a spring-biased presser that engages with a concave portion of the transmission. The concave portion includes a first concave portion with which the presser engages in a first driving state, and a second concave portion with which the presser engages in a second driving state.

The invention claimed is: 
     
       1. A valve mechanism for an engine, the valve mechanism comprising:
 a camshaft including a valve driving cam that drives one of an intake valve and an exhaust valve; 
 a rocker arm that converts a rotation of the valve driving cam into a reciprocal motion and transmits the reciprocal motion to one of the intake valve and the exhaust valve; 
 a synchronization cam that rotates in synchronism with the valve driving cam; and 
 a switch assembly including a cam follower that is pressed and moved by the synchronization cam, and that switches, when the cam follower is pressed by the synchronization cam, a driving state of one of the intake valve and the exhaust valve to a first driving state or a second driving state; wherein 
 the synchronization cam presses the cam follower at a time when one of the intake valve and the exhaust valve is closed; 
 the switch assembly includes:
 a switch unit that switches the driving state when a switch moves; 
 a driver including a transmission that transmits a motion of the cam follower to the switch, and drives the switch via the transmission in a direction to switch the driving state; and 
 a positioner that includes a presser that engages with a concave portion in the transmission, and positions the transmission at a predetermined position defined by the concave portion; 
 
 the concave portion includes:
 a first concave portion with which the presser engages when the transmission moves to a position in the first driving state; and 
 a second concave portion with which the presser engages when the transmission moves to a position in the second driving state; and 
 
 a positioning interval between the first concave portion and the second concave portion is greater than a moving amount of the transmission when the transmission is driven and moved by the synchronization cam. 
 
     
     
       2. The valve mechanism according to  claim 1 , wherein the concave portion has a slope such that an opening width becomes narrower from an opening edge to a bottom;
 a position to which the transmission is driven and moved by the synchronization cam is a position that the presser abuts against the slope of the concave portion; and 
 the transmission is further moved by a thrust generated when the presser presses against the slope, and reaches a predetermined position defined by the concave portion. 
 
     
     
       3. The valve mechanism according to  claim 2 , further comprising a spring having a spring force that biases the presser and is set to a magnitude that causes the transmission to be moved by the thrust to the predetermined position within a time when one of the intake valve and the exhaust valve is closed. 
     
     
       4. The valve mechanism according to  claim 1 , further comprising a spring having a spring force that biases the presser and is set to a magnitude that generates a position holding force that holds the transmission in the predetermined position defined by the concave portion in a state in which the presser engages with one of the first concave portion and the second concave portion; and
 the position holding force is set to a magnitude that prevents the first driving state and the second driving state from being switched by a force other than an actuating force generated when the synchronization cam presses the cam follower. 
 
     
     
       5. The valve mechanism according to  claim 1 , wherein the driver includes:
 a pivot shaft that rotates when a pressing force is transmitted from the cam follower; 
 an inverter that alternately switches a direction of the rotation of the pivot shaft between a first side and a second side; and 
 a converter that converts a pivotal motion of the pivot shaft into a reciprocal motion and transmits the reciprocal motion to the switch. 
 
     
     
       6. The valve mechanism according to  claim 5 , wherein the pivot shaft includes:
 a first projection projecting to a first side of a direction perpendicular or substantially perpendicular to an axial direction of the pivot shaft; and 
 a second projection projecting to a second side of the direction perpendicular or substantially perpendicular to the axial direction of the pivot shaft; 
 the inverter includes:
 a slide pin pressed by the cam follower; 
 a moving member that supports the slide pin movably in a first direction that is a moving direction of the cam follower, and movable in a second direction perpendicular or substantially perpendicular to the first direction; and 
 an actuator that drives the moving member to the first side or the second side of the second direction; 
 
 the slide pin is disposed between the cam follower and the first projection when the moving member moves to the first side of the second direction, and is disposed between the cam follower and the second projection when the moving member moves to the second side of the second direction; 
 one of the first projection and the second projection that interposes the slide pin between the one projection and the cam follower receives the pressing force, via the slide pin, from the cam follower pressed by the synchronization cam, and causes the pivot shaft to rotate in a direction in which the one projection is pressed; and 
 the other of the first projection and the second projection functions as a cam follower return cam that presses the slide pin toward the camshaft together with the cam follower and returns the cam follower when the slide pin that presses the one projection moves together with the moving member in a direction toward the other projection.